Securely provision endpoints on a hosted PBX

Polycom phones support HTTPS for provisioning however the OPP endpoint manager only lists http as an option when configuring it.

I am wondering how to restrict access to https connections and where to setup the user credentials for this if other than the linux user configs.

Is what I am trying to do possible? since the sip credentials are in the config files I want to be sure that they are secured in transit. If this is not possible I will work out another solution but it would be nice.
Thanks, Tim